The present invention relates to a method for making a metal sheet comprising a steel substrate, at least one face of which is coated with a metal coating comprising Al, the remainder of the metal coating being Zn and inevitable impurities.
Such a metal sheet is more particularly intended for making body parts for a land motor driven vehicle such as an automobile.
The metal sheet is then cut out and deformed in order to form the body parts or the body.
This body is then coated with a film of paint (or paint system) which ensures a good aspect of the surface and participates with the metal coating based on zinc, in protection against corrosion.
Coatings based on zinc of metal sheets have what is called a waviness of their outer surfaces, which can presently only be compensated by significant thicknesses of paint, under the penalty of having a so-called “orange peel” aspect, unacceptable for body parts.
The waviness W of the outer surface of a coating is a smooth pseudo-periodic geometrical irregularity with quite long wavelength (0.8 to 10 mm) which is distinguished from roughness R which corresponds to geometrical irregularities with short wavelengths.